Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $119.83   12.268%   $134.5307   $134.53   $134.55   $134.50  
  Purchase #2 $132.67   7.537%   $142.6693   $142.67   $142.65   $142.70  
  Purchase #3 $139.26   13.823%   $158.5099   $158.51   $158.50   $158.50  
  Purchase #4 $57.81   3.373%   $59.7599   $59.76   $59.75   $59.80  
  Purchase #5 $194.74   9.365%   $212.9774   $212.98   $213.00   $213.00  
  Purchase #6 $167.74   5.362%   $176.7342   $176.73   $176.75   $176.70  
  Purchase #7 $15.34   13.810%   $17.4585   $17.46   $17.45   $17.50  
  7 purchase totals = $827.39       $902.6399   $902.64   $902.65   $902.70